A temperature dependence kinetic study of O(1D) + CH4: overall rate coefficient and product yields.
Using a recently-developed chemiluminescence technique for monitoring O(1D), the rate coefficient, k1, of the important atmospheric reaction O(1D) + CH4 --> products has been determined over a wide temperature range, 227 to 450 K. The rate coefficient was shown to be independent of temperature, having a value of (1.91 +/- 0.08) x 10(-10) cm3 s(-1); the quoted uncertainties are with 95% confidence. This highly precise value, based on an extended set of determinations with very low scatter, is significantly greater, 26%, than current recommended values. Secondly, the fraction of O(1D) quenched to O(3P) by CH4, k(1q)/k1, was precisely determined from chemiluminescence decays over the temperature range 236 to 340 K. A temperature independent value for k(1q)/k1 of 0.002 +/- 0.003 was found. Finally, LIF detection of OH has been applied to accurately determine the product branching fraction to OH of O(1D) + CH4 at room temperature. Our value, k(1a)/k1 = 0.76 +/- 0.08 (95% confidence), is in line with recent determinations by other groups.
Vranckx
Stijn
S
University of Leuven, Department of Chemistry, Division of Quantum Chemistry and Physical Chemistry, Leuven, Belgium.
Peeters
Jozef
J
Carl
Shaun
S
D001272:Atmosphere; D007700:Kinetics; D008163:Luminescent Measurements / Q000295:instrumentation / Q000379:methods; D008697:Methane / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry*; D013696:Temperature; D013997:Time Factors
D008697:Methane; D010100:Oxygen